jimandme -

Figure on getting 1.5 - 2.0 hours of cooking time per green cylinder (assuming it's the 14-16 ounce variety frequently used with Coleman's).  If it was my group of 4, I'm figuring on 30 minutes of use per breakfast and 60 minutes per supper.  Over nine days, that's 8 breakfasts X 30 minutes = 240 minutes AND that's 8 suppers X 60 minutes = 480 minutes.  Grand total = 720 minutes or 12 hours of use.  So, that's 6 cylinders.

Of course, you may be cooking over a campfire for some meals.  For other meals you may only need to heat up a little water to pour into oatmeal or a bag of dehydrated food.  To the extent you do those things, your need for cylinders goes DOWN.  Frankly, I'd feel pretty safe with 5 cylinders (generally speaking) and possibly even 4.

On the other hand, your need for cylinders goes UP if you get one or two that develop "leaks".  I had two go bad on me on a single trip one year and found myself cooking over a campfire to compensate.  Fortunately, there was no fire ban going on.

Bottom line: it's something of a crap shoot.  You make your best guess re: actual cooking minutes, apply the burn time per cylinder, then hope you get lucky.

As for me, I've started using Kelly Kettles as my "back-up system."  For fixing coffee and simply heating water for eat-in-the-bag meals, you can't beat them.  You can cook on them, too, but not nearly as well as with gas. 

Jimbo   

I think mostly it comes down to what you're cooking and how you're cooking it.

Those propane "burn time" figures I was using DID seem a little "conservative" to me but they came straight from the manufacturer of those cylinders.  Re: using single vs. two-burner stoves, well... the way I look at it, using two burners uses propane twice as fast BUT requires approximately half the burn time.  In other words, feeding four people gets done in half-an-hour vs. an hour but, ultimately, uses about the same amount of fuel.

But I'm no cook, so what do I know?  I'm just doing the math.  There could easily be other considerations I'm simply not thinking of regarding fuel consumption.

However, we arrived at the number, it seems like both PD and I are saying you'd do well to pack 4 cylinders... and maybe toss in a 5th if you want to be extra safe.

Jimbo   

Another thought:  I recently purchased two of the new, large Coleman brand Butane cylinders which are supposed to work with MSR small burners.  They did work the first time I screwed a MSR burner on them and did just fine.  However I left the burner screwed in because I would use it for the next meal and was in camp.  The second time I tried to light the burner it did not want to light...seemed no gas was coming out.  This happened to me with both cylinders and two different MSR burners.  Worked fine the first time, but with burner left on would not light/pump fuel a few hours later when I wanted to cook something else.  Has anyone else had this happen to them?
The cylinders say "self sealing" so I am wondering if they might seal below the aperture which allows the burner to access the fuel when it is screwed into the canister?  My trip was nearing the end so I unscrewed the burners and brought them and cylinders home.  I have not had a chance to re-try them now to see if unscrewing the burners made a difference. 

PD, Thanks for some response.  No, the gas was still in the cylinders, in fact quite a lot of it.  Do not know the model of my stove; it is small and has a red triangular plastic tube case for travel.  Both stoves worked fine all summer with MSR or Optimus cylinders for fuel and worked fine for first run on the Coleman cylinders too.
Since I last tried using the stoves I have packed them away, and off the cylinders.  I just returned from the trip I was on and the stove/fuel are still packed away.  I will try them again when I get a chance and see if they want to work.

My own personal opinion is that all of the Butane/ Propane cylinders are manufactured in South Korea by the same company who private labels them as needed to the world.  The thread forms and seals are too uniform to be made by multiple vendors.  My guess would be you got a couple from the same bad lot.

MB